1. Technical Field
This invention relates generally to the field of semiconductor manufacturing. More particularly, the invention relates to devices and methods for removing polishing pads from the polishing platens of chemical mechanical planarization (CMP) machines.
2. Description of the Related Art
CMP is an abrasive process used to polish silicon wafers during semiconductor manufacturing. Polishing planarizes, or flattens, the surface of the wafer to very precise tolerances. A planarized wafer surface is essential for maintaining the precise photolithographic depth of focus required for integrated circuit chip fabrication.
CMP is typically performed using a machine having a platen, a polishing pad, a backing film, and a wafer carrier. The polishing pad resides on the platen, and a semiconductor wafer is pressed against the polishing pad. Backing film separates the wafer from the wafer carrier, which is used to hold the wafer in place during the CMP process. Once a wafer is mounted on a CMP device, a slurry consisting of liquid and small suspended particles, such as a colloidal silica suspended in a KOH solution, is applied at the interface of the pad and the wafer. The slurry uses mechanical and chemical processes to planarize the wafer.
During the CMP process, the polishing platen rotates. The wafer and the wafer carrier also rotate independent of the platen, causing the wafer to move through the slurry in a rotary fashion. As slurry flows over a wafer's surface, the suspended particles in the slurry mechanically abrade the surface and the liquid in the slurry chemically etches the abraded area. The pressure from the wafer carrier against the polishing pad provides the driving force for the process. In this manner, CMP removes materials from the high spots on the wafer while removing negligible amounts of material from the low spots on the wafer, resulting in a flattened, or planarized, wafer.
A critical component of the CMP process is the polishing pad. Polishing pads are typically made of polyurethane, and contain grooves or small perforations punched into the pads to help transport the slurry and facilitate polishing. The surface of the polishing pad contains asperites typically 1 to 10 micrometers in size that help transport and hold the slurry. With use, these asperites become flattened, resulting in a state called "glazing." A glazed pad reduces the efficiency of the CMP process because the pad cannot hold much polishing slurry, nor can it apply appropriate pressure to a wafer. Although a glazed pad can be rejuvenated, eventually all pads need to be replaced. Typically, pads require replacement after polishing just 1500 wafers, meaning that a pad's lifespan is approximately 50 hours at a polishing rate of 30 wafers per hour.
Conventionally, polishing pads are removed from platens manually, whereby an individual tears the pad off of the platen. This conventional method is unsatisfactory, however, because polishing pads are affixed to platens using a strong adhesive. Moreover, the conventional method cannot be performed by workers lacking the necessary physical strength to remove a polishing pad. The task can cause injury not only because of the force that is necessary to remove a polishing pad from a platen, but also because the task is ergonomically difficult. On average, approximately one hour is required to remove an old pad and replace it with a new one. Given this downtime, there is a great need for a device and an improved method for removing polishing pads from platens.